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Difference between revisions of "cpp/container/multimap"

From cppreference.com
< cpp‎ | container
m (langlinks)
(Added LWG issue #230 DR (part 7).)
Line 8: Line 8:
 
     class T,
 
     class T,
 
     class Compare {{=}} std::less<Key>,
 
     class Compare {{=}} std::less<Key>,
−
     class Allocator {{=}} std::allocator<std::pair<const Key, T> >
+
     class Allocator {{=}} std::allocator<std::pair<const Key, T>>
 
> class multimap;
 
> class multimap;
 
}}  
 
}}  
 
{{dcl|num=2|since=c++17|1=
 
{{dcl|num=2|since=c++17|1=
 
namespace pmr {
 
namespace pmr {
−
     template <class Key, class T, class Compare = std::less<Key>>
+
     template < class Key, class T, class Compare = std::less<Key> >
−
     using multimap = std::multimap<Key, T, Compare,
+
     using multimap = std::multimap<
−
                                  std::pmr::polymorphic_allocator<std::pair<const Key,T>>>;
+
        Key, T, Compare,
 +
        std::pmr::polymorphic_allocator<std::pair<const Key, T>>
 +
    >;
 
}
 
}
 
}}  
 
}}  
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Multimap is an associative container that contains a sorted list of key-value pairs, while permitting multiple entries with the same key. Sorting is done according to the comparison function {{tt|Compare}}, applied to the keys. Search, insertion, and removal operations have logarithmic complexity.
 
Multimap is an associative container that contains a sorted list of key-value pairs, while permitting multiple entries with the same key. Sorting is done according to the comparison function {{tt|Compare}}, applied to the keys. Search, insertion, and removal operations have logarithmic complexity.
  
−
The order of the key-value pairs whose keys compare equivalent is the order of insertion and does not change. {{mark since c++11}}
+
{{rrev|since=c++11|
 +
The order of the key-value pairs whose keys compare equivalent is the order of insertion and does not change.
 +
}}
  
−
Everywhere the standard library uses the {{named req|Compare}} requirements, equivalence is determined by using the equivalence relation as described on {{named req|Compare}}. In imprecise terms, two objects {{tt|a}} and {{tt|b}} are considered equivalent if neither compares less than the other: {{tt|!comp(a, b) && !comp(b, a)}}.
+
Everywhere the standard library uses the {{named req|Compare}} requirements, equivalence is determined by using the equivalence relation as described on {{named req|Compare}}. In imprecise terms, two objects {{c|a}} and {{c|b}} are considered equivalent if neither compares less than the other: {{c|!comp(a, b) && !comp(b, a)}}.
  
 
{{tt|std::multimap}} meets the requirements of {{named req|Container}}, {{named req|AllocatorAwareContainer}}, {{named req|AssociativeContainer}} and {{named req|ReversibleContainer}}.
 
{{tt|std::multimap}} meets the requirements of {{named req|Container}}, {{named req|AllocatorAwareContainer}}, {{named req|AssociativeContainer}} and {{named req|ReversibleContainer}}.
 +
 +
===Template parameters===
 +
{{todo|Add descriptions of the template parameters.}}
  
 
===Member types===
 
===Member types===
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===[[cpp/container/multimap/deduction_guides|Deduction guides]]{{mark since c++17}}===
 
===[[cpp/container/multimap/deduction_guides|Deduction guides]]{{mark since c++17}}===
 +
 +
===Defect reports===
 +
{{dr list begin}}
 +
{{dr list item|wg=lwg|dr=230|std=C++98|before={{tt|Key}} was not required to be {{named req|CopyConstructible}}<br>(a key of type {{tt|Key}} might not be able to be constructed)|after={{tt|Key}} is also required to<br>be {{named req|CopyConstructible}}}}
 +
{{dr list end}}
  
 
{{langlinks|de|es|fr|it|ja||pl|pt|ru|zh}}
 
{{langlinks|de|es|fr|it|ja||pl|pt|ru|zh}}

Revision as of 00:29, 12 October 2022

 
C++
 
Containers library
 
std::multimap
Member functions
Non-member functions
(until C++20)(until C++20)(until C++20)(until C++20)(until C++20)
Deduction guides(C++17)
 
Defined in header <map>
template<

    class Key,
    class T,
    class Compare = std::less<Key>,
    class Allocator = std::allocator<std::pair<const Key, T>>

> class multimap;
 (1)
namespace pmr {

    template < class Key, class T, class Compare = std::less<Key> >
    using multimap = std::multimap<
        Key, T, Compare,
        std::pmr::polymorphic_allocator<std::pair<const Key, T>>
    >;

}
 (2) (since C++17)

Multimap is an associative container that contains a sorted list of key-value pairs, while permitting multiple entries with the same key. Sorting is done according to the comparison function Compare, applied to the keys. Search, insertion, and removal operations have logarithmic complexity.

The order of the key-value pairs whose keys compare equivalent is the order of insertion and does not change.

(since C++11)

Everywhere the standard library uses the Compare requirements, equivalence is determined by using the equivalence relation as described on Compare. In imprecise terms, two objects a and b are considered equivalent if neither compares less than the other: !comp(a, b) && !comp(b, a).

std::multimap meets the requirements of Container, AllocatorAwareContainer, AssociativeContainer and ReversibleContainer.

Contents

Template parameters

This section is incomplete
Reason: Add descriptions of the template parameters.

Member types

Member type Definition
key_type Key[edit]
mapped_type T[edit]
value_type std::pair<const Key, T>[edit]
size_type Unsigned integer type (usually std::size_t)[edit]
difference_type Signed integer type (usually std::ptrdiff_t)[edit]
key_compare Compare[edit]
allocator_type Allocator[edit]
reference value_type&[edit]
const_reference const value_type&[edit]
pointer

Allocator::pointer

(until C++11)

std::allocator_traits<Allocator>::pointer

(since C++11)
[edit]
const_pointer

Allocator::const_pointer

(until C++11)

std::allocator_traits<Allocator>::const_pointer

(since C++11)
[edit]
iterator LegacyBidirectionalIterator to value_type[edit]
const_iterator LegacyBidirectionalIterator to const value_type[edit]
reverse_iterator std::reverse_iterator<iterator>[edit]
const_reverse_iterator std::reverse_iterator<const_iterator>[edit]
node_type (since C++17) a specialization of node handle representing a container node[edit]

Member classes

 compares objects of type value_type
(class) [edit]

Member functions

 constructs the multimap
(public member function) [edit]
destructs the multimap
(public member function) [edit]
assigns values to the container
(public member function) [edit]
returns the associated allocator
(public member function) [edit]
Iterators
(C++11)
 returns an iterator to the beginning
(public member function) [edit]
(C++11)
 returns an iterator to the end
(public member function) [edit]
(C++11)
 returns a reverse iterator to the beginning
(public member function) [edit]
(C++11)
 returns a reverse iterator to the end
(public member function) [edit]
Capacity
checks whether the container is empty
(public member function) [edit]
returns the number of elements
(public member function) [edit]
returns the maximum possible number of elements
(public member function) [edit]
Modifiers
clears the contents
(public member function) [edit]
inserts elements or nodes(since C++17)
(public member function) [edit]
(C++11)
 constructs element in-place
(public member function) [edit]
(C++11)
 constructs elements in-place using a hint
(public member function) [edit]
erases elements
(public member function) [edit]
swaps the contents
(public member function) [edit]
(C++17)
 extracts nodes from the container
(public member function) [edit]
(C++17)
 splices nodes from another container
(public member function) [edit]
Lookup
returns the number of elements matching specific key
(public member function) [edit]
finds element with specific key
(public member function) [edit]
(C++20)
 checks if the container contains element with specific key
(public member function) [edit]
returns range of elements matching a specific key
(public member function) [edit]
returns an iterator to the first element not less than the given key
(public member function) [edit]
returns an iterator to the first element greater than the given key
(public member function) [edit]
Observers
returns the function that compares keys
(public member function) [edit]
returns the function that compares keys in objects of type value_type
(public member function) [edit]

Non-member functions

(removed in C++20)(removed in C++20)(removed in C++20)(removed in C++20)(removed in C++20)(C++20)
 lexicographically compares the values of two multimaps
(function template) [edit]
specializes the std::swap algorithm
(function template) [edit]
(C++20)
 erases all elements satisfying specific criteria
(function template) [edit]

Deduction guides(since C++17)

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 230 C++98 Key was not required to be CopyConstructible
(a key of type Key might not be able to be constructed) 		Key is also required to
be CopyConstructible
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